1. Field of the Invention
The present invention relates to a ceramic material and a sputtering target member, and more specifically to a ceramic material and a sputtering target member containing magnesium oxide as a main component.
2. Description of the Related Art
Magnesium oxide (MgO) has been used for refractories, additives, electronic components, fluorescent materials, raw materials for target members, raw materials for superconducting thin film bases, tunnel barriers of magnetic tunnel junction elements (hereafter, MTJ elements), protective films for color plasma display panels (PDPs), and the like and have received attention as a material for a very wide range of uses. In particular, sputtering target members are used for forming tunnel barriers of MTJ elements that use a tunneling magnetoresistance effect. The tunneling magnetoresistance effect is a resistance-change phenomenon that occurs, in an MTJ element in which a very thin insulator with a thickness of several nanometers is sandwiched between two magnetic layers, when the relative directions of magnetization of the two magnetic layers are parallel or antiparallel. The tunneling magnetoresistance effect is applied to, for example, a magnetic head of a hard disk using a change in electrical resistance in the magnetization states.
In recent years, magnetoresistive random access memory (hereafter, MRAM) that uses the above-described MTJ elements has been studied (e.g. refer to PTL 1). In MRAM, for example, many MTJ elements are arranged and the magnetization alignment of each of the MTJ elements is used for an information carrier. MRAM has characteristics such as non-volatility, high-speed operation, and high endurance for many writings, and thus has been developed as memory that surpasses known semiconductor memories (e.g., SRAM and DRAM). Memories whose storage capacity is several megabits (Mbit) to several tens of megabits (Mbit) have been made on an experimental basis so far. However, the storage capacity needs to be further increased to a gigabit (Gbit) level to replace, for example, DRAM with MRAM.
Single crystal MgO or high-purity MgO have been generally used for film bodies of tunnel barriers of MTJ elements, and such a tunnel barrier has been generally formed by sputtering with a sputtering target member composed of a high-purity MgO sintered body. In recent years, however, an insulating film in which the tunneling magnetoresistance can be artificially changed by using a tunnel barrier in which part of MgO is replaced has been developed (e.g., refer to PTL 2 and PTL 3).